1. Field of the Invention
This invention relates to an integrated optics semiconductor laser device comprising a light emitting means, a diffraction grating for controlling the wavelength of a produced laser beam, and an optical amplifier, which are combined with one another. This invention particularly relates to an integrated optics semiconductor laser device, wherein adverse effects of an optical wave returning from an end face of the optical amplifier are kept small.
2. Description of the Prior Art
There have heretofore been proposed various semiconductor laser devices, which have a high output power and are controlled to produce a laser beam in a fundamental transverse mode. One example of such semiconductor laser devices is an integrated optics semiconductor laser device disclosed in, for example, U.S. Pat. No. 4,744,089. The disclosed integrated optics semiconductor laser device comprises, combined together, a master generator, which is constituted of a distributed feedback laser (hereinbelow referred to as the DFB laser) having a diffraction grating for controlling the wavelength of the produced laser beam, and an optical amplifier, which has a tapered (i.e., progressively widened) active region and has an anti-reflection film coated on an optical wave radiating end face.
Also, for example, Japanese Unexamined Patent Publication No. 5(1993)-218594 discloses an integrated optics semiconductor laser device comprising a DFB generator, a pre-amplifier, and an optical amplifier having a tapered active region, which are respectively provided with independent electrical contacts and are driven by independent current sources. With the disclosed constitution, the control operation range for the laser beam radiated from the generator can be kept wide, and the oscillation in the fundamental transverse mode can be carried out on a comparatively high level.
Further, a different example of an integrated optics semiconductor laser device is proposed in, for example, "IEEE Journal of Quantum Electronics," Vol. 29, No. 6, pp. 2052-2057, 1993. The proposed integrated optics semiconductor laser device comprises a master generator, in which the wavelength of a produced laser beam is controlled by a diffraction grating as described above, and an optical amplifier, which is combined with the master generator.
Furthermore, for example, U.S. Pat. No. 4,856,017 discloses an integrated optics semiconductor laser device comprising (i) an optical amplifier provided with a tapered active gain medium layer, which has a wide output face coated with an anti-reflection film at one end and has a comparatively narrow region at the other end, the comparatively narrow region undergoing oscillation in the fundamental transverse mode, (ii) a diffraction grating for controlling the wavelength of a produced laser beam, and (iii) a means for causing a wavelength-dependent feedback to occur in the active gain medium layer.
However, the conventional integrated optics semiconductor laser devices having an optical amplifier, in which an optical wave is guided through the tapered active medium portion as described above, have the drawbacks in that they cannot always be controlled to produce a laser beam in the fundamental transverse mode under the conditions for radiating a laser beam having a high intensity. In "IEEE Journal of Quantum Electronics," Vol. 29, No. 6, pp. 2052-2057, 1993, it is reported that a diffraction limit optical wave of a 2 W level was achieved. However, actually, only the products having an output power of at most 1 W level have heretofore been used in practice.